Question

I keep getting an SWTException that says “Invalid Thread Access” when I try and run my code. I read up and the problem seems to be having code which tries to access SWT objects from outside the UI thread. Specifically I have a table widget and I have added a selection listener. Here is the code for the selection listener.

rosterTable.addSelectionListener(new SelectionAdapter()

    {
        public void widgetSelected(final SelectionEvent event)
        {

              createChat(connection,event);


        }

            });

and here is the code for the createChat method:

public void createChat(final XMPPConnection connection,final SelectionEvent event)
{
    Display.getDefault().syncExec(new Runnable()        
    {
        public void run()
        {
            String s = event.item.toString();
            int length = event.item.toString().length();
            ClassView cv = new ClassView(connection,s.substring(11,length -1),null);
        }
    });

As you can see I’ve tried too synchronise the code which is outside the UI thread, with the UI thread by wrapping it in the syncExec method but I still get the exception when the table item is selected which leads me to believe I have put the syncExec part in the wrong place.

I also thought the problem may be coming from the fact that the ClassView object that is instantiated in the createChat method uses SWT widgets, but I am not sure.

Does anyone one know where the syncExec code should go?

Or if I am doing it completely wrong, how I can fix it?

Update:

I did what you said and unfortunately I’m still getting the exception, I did a bit of redesign on the code so it looks a little different now, I don’t think it should make any difference but just in case here’s the code for the listener again:

 rosterTable.addSelectionListener(new SelectionAdapter()

    {
        public void widgetSelected(final SelectionEvent event)
        {

           selectedUser = event.item.toString();
           System.out.println(selectedUser);
           rm.createChat(selectedUser);

        }






    });

and here’s the code for the method which is in a different class now:

public void createChat(String item)
{
    int length = item.length();
    Chatter c = new Chatter(connection,item.substring(11,length-1));

}

Here’s a stack trace for the exception:

org.eclipse.swt.SWTException: Invalid thread access
at org.eclipse.swt.SWT.error(SWT.java:3884)
at org.eclipse.swt.SWT.error(SWT.java:3799)
at org.eclipse.swt.SWT.error(SWT.java:3770)
at org.eclipse.swt.widgets.Display.checkDisplay(Display.java:721)
at org.eclipse.swt.widgets.Display.create(Display.java:783)
at org.eclipse.swt.graphics.Device.<init>(Device.java:135)
at org.eclipse.swt.widgets.Display.<init>(Display.java:454)
at org.eclipse.swt.widgets.Display.<init>(Display.java:445)
at instantmessengerplugin.ClassView.<init>(ClassView.java:33)
at instantmessengerplugin.Chatter.<init>(Chatter.java:20)
at instantmessengerplugin.RosterManager.createChat(RosterManager.java:48)
at instantmessengerplugin.RosterView$1.widgetSelected(RosterView.java:103)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3880)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3473)
at instantmessengerplugin.RosterView.<init>(RosterView.java:158)
at instantmessengerplugin.Connection.connect(Connection.java:110)
at instantmessengerplugin.Connection$1.widgetSelected(Connection.java:65)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3880)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3473)
at instantmessengerplugin.Connection.<init>(Connection.java:77)
at instantmessengerplugin.Connection.main(Connection.java:119)

Answer 1

I fixed the problem. The exception was coming from the fact that in ClassView I was trying to create a instance of class SWT Display, when there was already another instance of it in existence. The platform only allows one to open at any one time.

I have altered the code so that only one display is used and the exception is gone.

Thank you for all your help.